JPH05308219A - Microwave detector - Google Patents

Abstract

PURPOSE:To realize the inexpensive and small sized microwave detector by combining a microwave circuit component whose lower face is open on a printed circuit board so as to form a horn antenna and a cavity. CONSTITUTION:A microwave circuit component 12 whose lower face is open is mounted onto a printed circuit board 10 so as to cover a metallic film 11 thereof. Thus, a horn antenna and a cavity are formed. A microwave substrate 17 for a 1st local oscillator is contained in the cavity and a mixer diode 14 is mounted onto a throat of the horn antenna. An intermediate frequency processing circuit section 18 is mounted onto a lower side of a mount point of the mixer diode 14 and the circuit 18 is covered by a shield case 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave detector for detecting and notifying a microwave emitted from a measuring instrument, and more particularly to a reception frequency for frequency-mixing a radio wave received by a horn antenna and an output of a local oscillator. Regarding the structure of the conversion unit.

[0002]

2. Description of the Related Art A microwave detector configured to detect a microwave emitted from a radar type speed measuring instrument and issue an alarm is conventionally known. In the case of a general radar type speed measuring instrument for traffic monitoring, 10G
Hz band (X band), 24 GHz band (K band), 35
A microwave in any band of the GHz band (Ka band) is used. A microwave detector having a speed measuring instrument of this type as a detection target device receives a microwave of a predetermined band by a superheterodyne circuit having the following configuration.

A horn antenna is generally used as a receiving antenna. A mixer diode is installed at the feeding point of the throat portion of the horn antenna. In addition, a microwave circuit forming a local oscillator is provided at the back of the throat portion of the horn antenna. The frequency of the signal received by the horn antenna and the output of the local oscillator are mixed by the mixer diode. Further, an appropriate filter is provided between the mixer stage and the local oscillator so that the reception input by the horn antenna does not adversely affect the operation of the local oscillator. A type in which a mixer and a local oscillator are configured by a three-dimensional circuit using a waveguide and a type in which a mixer portion and a local oscillator are configured by a microwave integrated circuit using a microstrip line are known.

A typical structure of a microwave detector of this kind is shown in Japanese Patent Publication No. 500944 of 1986. The outline of the prior art is shown in FIG.

In the structure shown in FIG. 1, an aluminum die-cast antenna component 2 having an open lower surface is screwed to the upper surface of the printed wiring board 1. Printed wiring board 1
A metal film (copper foil) 3 is formed in a predetermined pattern on the upper surface of the antenna component 2, and the antenna component 2 is attached so as to cover the metal film 3 and the lower surface of the antenna component 2 opened by the metal film 3. Will be blocked. In the antenna component 2, not only the horn antenna portion 2a but also two shield case portions 2b and 2c are integrally formed, and the shield case portion 2b is connected to the back of the throat portion of the horn antenna portion 2a.

The horn antenna portion 2a having an opened lower surface does not function as a horn antenna by itself, but it is mounted on the printed wiring board 1 and the opened lower surface of the horn antenna portion 2a is covered with the metal film 3 to form the horn. Functions as an antenna.

Printed wiring board 1 and shield case 2
The microwave integrated circuit 4 is housed in the space surrounded by b. The microwave integrated circuit 4 includes a first local oscillator (not shown) on a dielectric substrate and a mixer diode 4 for outputting its output.
of the microstrip line leading to b, the ridge 2d integrally formed in the center of the horn antenna section 2a, and the feed strip 4a receiving the antenna input, and the output of the first local oscillator and the antenna input. First intermediate frequency filter 4c to which the frequency mixed output is input
Have been implemented.

Shield case 2 on printed wiring board 1
Although not shown in the drawing, the portion covered by c has a second local oscillator, a second frequency mixing circuit for frequency mixing the second local oscillation output and the output of the microwave integrated circuit 4, and a second frequency mixing circuit. A filter having an output of the circuit as an input is mounted (these circuits are referred to as an intermediate frequency processing circuit unit 5). The lower surface of the printed wiring board 1 includes a detection circuit that detects the output of the intermediate frequency processing circuit unit 5, a discrimination circuit that discriminates a predetermined reception signal from the detection output, and an alarm circuit that issues an alarm signal in response to the discrimination output. Implemented on the side.

[0009]

As shown in FIG. 1, the structure in which the metal film 3 formed on the printed wiring board 1 is a part of the constituent elements of the horn antenna is an antenna component which completely functions as a horn antenna. This is advantageous in terms of cost as compared with the structure using, and is also advantageous in terms of downsizing of the device. Further, in the above-described conventional technique, the microwave integrated circuit 4 is provided with the first local oscillator, the first frequency mixing circuit, and the intermediate frequency filter, and the input of the horn antenna, which is a three-dimensional circuit, is a planar circuit. It is configured to be injected into the four feed strips 4a. Microwave integrated circuits using microstrip lines are certainly excellent in terms of miniaturization and adjustment-free, but it is necessary to make the pattern precision of the microstrip conductor on the dielectric substrate fine, and advanced design technology Is required,
It is rather disadvantageous in terms of work precision and part yield. In particular, a very advanced technique is required for the relationship between the ridge 2d and the feed strip 4a for efficiently injecting the antenna input into the microwave integrated circuit. In that respect, in the case of a three-dimensional circuit using a waveguide, the characteristics can be easily adjusted by a matching means such as an iris or a pin after the three-dimensional circuit body is manufactured. Therefore, a three-dimensional circuit is advantageous in terms of ease of design and manufacture.

Further, in the conventional configuration of FIG. 1, since the intermediate frequency filter 4c in the microwave integrated circuit 4 is exposed to the antenna input and the output of the first local oscillator, there is an adverse effect such as generation of noise depending on the frequency. receive.
Further, the upper surface side of the intermediate frequency processing circuit unit 5 is covered with the shield case 2c, but in order to shield the lower surface side as well, a metal film for shielding must be formed on the lower surface side of this portion of the printed wiring board 1. There is. Then, the lower surface side of this portion cannot be used for mounting other circuits. Therefore, the entire substrate area must be increased. Further, there is a problem that the connecting means for transmitting the output of the microwave integrated circuit 4 in the shield case portion 2b to the intermediate frequency processing circuit portion 5 in the shield case portion 2c is troublesome. For example, when a wiring pattern extending from the microwave integrated circuit 5 to the intermediate frequency processing circuit unit 5 is formed on the upper surface side of the printed wiring board 1, the pattern and the antenna component 2 must be insulated. Further, for example, a pin or an eyelet is used to make a through connection from the front surface of the microwave integrated circuit 4 to the back surface of the printed wiring board 1, and the wiring pattern on the lower surface of the board 1 guides it to below the intermediate frequency processing circuit section 5, where it is pinned again. It is necessary to connect it to the intermediate frequency processing circuit section 5 on the upper surface side of the substrate 1 by means of, for example, eyelet or through hole processing. In any case, it is very troublesome.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to use a metal film formed on a printed wiring board as a part of components of a horn antenna and a microwave stereo circuit. It is a wave detector, and the first frequency mixing unit and its peripheral circuit, and the second frequency mixing unit and its peripheral circuit can be mounted in a small size with a simple structure.

[0012]

Therefore, in the present invention, the antenna and the reception frequency converter of the microwave detector are constructed by the following structures.

A metal three-dimensional circuit component having an opened lower surface is attached to an upper surface of the printed wiring board, and the opened lower surface of the three-dimensional circuit component is closed by a metal film formed on the upper surface of the substrate. The three-dimensional circuit component and the metal film form a horn antenna and a cavity connected to the back of the throat portion of the horn antenna.

A mixer diode is mounted at a feeding point of the throat portion of the horn antenna and sandwiched between the three-dimensional circuit component and the printed wiring board.

A first local oscillator mounted on a microwave circuit board is housed in the cavity.

The output terminal of the mixer diode penetrates to the lower surface side of the printed wiring board at the mounting position, and the first intermediate frequency filter, the second mixer circuit, and the second mixer circuit are provided around the penetration point on the lower surface of the board. An intermediate frequency processing circuit unit including a two local oscillator is mounted.

A shield case is attached to the lower surface of the printed wiring board so as to cover the intermediate frequency processing circuit section.

[0018]

The horn antenna and the cavity are formed by the above-mentioned three-dimensional circuit component and the metal film on the printed wiring board, the first local oscillator is housed in the cavity, and the output and the antenna input are in the three-dimensional circuit mode. The frequency is mixed by the mixer diode. The output terminal of the mixer diode penetrates the lower surface side of the printed wiring board at its attachment point and is introduced into the intermediate frequency processing circuit section mounted on the lower surface side of the board. The intermediate frequency processing circuit section is covered by the shield case attached to the lower surface side of the substrate and completely shielded by the metal film on the upper surface side.

[0019]

2 and 3 show the structure of a microwave detector according to an embodiment of the present invention. A metal film (copper foil) 11 having a large area is formed in a predetermined pattern on the upper surface side of the rectangular printed wiring board 10. The aluminum die-cast three-dimensional circuit component 12 is attached by a screw so as to cover the metal film 11 portion of the printed wiring board 10. The three-dimensional circuit component 12 has a horn antenna portion 12a and a cavity portion 12b, but the lower surface is completely opened. By mounting this on the printed wiring board 10, the opened lower surface of the three-dimensional circuit component 12 is the metal film 11. Blocked by. By mounting the three-dimensional circuit component 12 on the printed wiring board 10 in this manner, a horn antenna and a cavity connected to the back of the throat portion are formed. Further, screw type pin matching devices 20a and 20b are attached near the horn antenna throat portion of the three-dimensional circuit component 12.

The horn antenna section 12 of the three-dimensional circuit component 12
A boss portion 12c is formed integrally with the throat portion of a, and the printed wiring board 10 facing the boss portion 12c is formed.
A through hole 13 is formed on the side. A pin-shaped leg portion of a metal base 15 is fitted into the through hole 13 via a spring washer 16. The hole on the upper surface side of the pedestal 15 and the hole of the boss portion 12c are on the same axis, and the pin portions at both ends of the pill type mixer diode 14 are the boss portion 1.
2c and the pedestal 15 are fitted respectively. As a result, the mixer diode 14 is arranged at the feeding point of the throat portion of the horn antenna while being sandwiched between the printed wiring board 10 and the three-dimensional circuit component 12.

A microwave substrate 17 is housed in a cavity surrounded by the metal film 11 of the printed wiring board 10 and the cavity portion 12b of the three-dimensional circuit component 12. A first local oscillator is mounted on the microwave board 17. The oscillation output of the first local oscillator is radiated into the space inside the cavity and reaches the throat portion of the horn antenna.
The mixer diode 14 is arranged in this throat portion, and the antenna input and the first local oscillation output are frequency-mixed in the cubic circuit mode.

Pedestal 1 for mounting mixer diode 14
5 also serves as a terminal of the mixer diode 14. That is, the output of the mixer diode 14 is guided to the lower surface side of the board 10 via the pedestal 15 fitted in the through hole 13 of the printed wiring board 10.

The intermediate frequency processing circuit section 1 is provided on the lower surface of the printed wiring board 10 in the peripheral portion of the through hole 13.
8 is mounted by the planar mounting method. The intermediate frequency processing circuit unit 18 has a first intermediate frequency filter having the output of the mixer diode 14 as an input, a second local oscillator,
A second mixer circuit for frequency mixing the second local oscillation output and the output of the first intermediate frequency filter is included. Then, the shield case 19 is attached to the lower surface side of the printed wiring board 10 so as to cover the intermediate frequency processing circuit portion 18.

The pattern of the metal film 11 on the upper surface side of the printed wiring board 10 not only closes the opening on the lower surface of the three-dimensional circuit component 12, but also functions as a shield for the intermediate frequency processing circuit section 18. Is set. Further, as shown in the figure, the shield case 19 on the lower surface and the three-dimensional circuit component 12 on the upper surface can be attached to the printed wiring board 10 with the same screw. Although not shown, a detection circuit, a received signal discrimination circuit,
Low frequency circuits such as alarm circuits are printed wiring board 10
To be implemented in other areas of.

FIG. 4 shows a modification of the embodiment shown in FIGS. 2 and 3. Here, a trimmer resistor 21 for sweep adjustment of the second local oscillator included in the intermediate frequency processing circuit section 18 on the lower surface side of the printed wiring board 10 is attached to the upper surface side of the printed wiring board 10 through a through hole.

FIG. 5 shows a configuration example in which the position of the intermediate frequency processing circuit portion 18 on the lower surface of the printed wiring board 10 is slightly different from that of the above embodiment. Thus, the intermediate frequency processing circuit section 18 may be provided at an appropriate position around the through hole 13 to which the mixer diode 14 is attached.

[0027]

As described in detail above, in the present invention, the metal film formed on the upper surface of the printed wiring board is used as a part of the constituent elements of the horn antenna, and the cavity connected to the depth of the throat portion of the horn antenna. The antenna input and the first local oscillation output are frequency-mixed in the three-dimensional circuit mode.
Therefore, unlike the conventional technique using the microwave integrated circuit operating in the planar circuit mode, the operating characteristics of the antenna and the frequency mixing unit can be simplified by a simple adjusting means such as a pin matching device provided in a required part of the three-dimensional circuit. The design, production and adjustment are easy and the cost can be reduced. In addition, the terminals of the mixer diode attached to the throat of the horn antenna penetrate to the lower surface side of the printed wiring board, the intermediate frequency processing circuit section is mounted around the penetration point, and the circuit section is attached to the lower surface of the board. Covered with a case. Therefore, the mixer diode and the intermediate frequency processing circuit section can be connected very easily by the shortest path, and the first intermediate frequency filter is not exposed to the antenna input or the first local oscillation output, thereby achieving a good operation without noise. Can be realized.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a structure of a conventional microwave detector.

FIG. 2 is an exploded perspective view showing the structure of the microwave detector according to the embodiment of the present invention.

FIG. 3 is an exploded perspective view showing a structure on a lower surface side of the printed wiring board in FIG.

FIG. 4 is an exploded perspective view showing a structure of a microwave detector according to another embodiment of the present invention.

FIG. 5 is an exploded perspective view showing the structure of the lower surface side of the printed wiring board in the microwave detector according to another embodiment of the present invention.

[Explanation of symbols]

 10 printed wiring board 11 metal film 12 three-dimensional circuit component 12a horn antenna section 12b cavity section 12c boss section 13 through hole 14 pill type mixer diode 15 pedestal 16 spring washer 17 microwave board 18 intermediate frequency processing circuit section 19 shield case 20a, 20b Pin matching device 21 Trimmer resistor

Claims (1)

[Claims] 1. A microwave detector comprising an antenna and a reception frequency conversion unit having the following structures. A three-dimensional circuit component made of metal whose lower surface is opened is attached to the upper surface of the printed wiring board, and the opened lower surface of the three-dimensional circuit component is closed by the metal film formed on the upper surface of this substrate. The circuit component and the metal film form a horn antenna and a cavity connected to the back of the throat portion of the horn antenna. Located at the feeding point of the throat part of the horn antenna,
A mixer diode is attached in a state of being sandwiched between the three-dimensional circuit component and the printed wiring board. A first local oscillator mounted on a microwave circuit board is housed in the cavity. The output terminal of the mixer diode penetrates the lower surface side of the printed wiring board at the mounting position,
An intermediate frequency processing circuit unit including a first intermediate frequency filter, a second mixer circuit, and a second local oscillator is mounted around the through point on the lower surface of the substrate. A shield case is attached to the lower surface side of the printed wiring board so as to cover the intermediate frequency processing circuit section.